Suppose that for every root canal case from the previous 18 months, 3 controls were selected and both cases (43) and controls (129) were asked the about various exposures.

a.Fill in the ORs for all the exposures in the table below (counts in the table are for those patients who had the exposure). For each OR use the odds of having the particular exposure in cases compared to controls.

exposure

Cases

Controls

OR

Have gum disease

15

10

Chew sugarless gum

6

20

Floss regularly

10

65

Taken antibiotics in previous 6 months

5

36

Overweight/obese

20

38

Recent viral infection

17

51

b.Which of these exposures appear to be protective and which appear harmful?

c.What doesn't appear to have any association?

d.If the cases are those from the first study how does that impact your interpretation of the above ORs?

e.If the controls are a random selection of anyone who did not have a filling in a molar vs. those who did, how might that impact the ORs?

f.If the general population was used for controls (vs. those with a filling in a molar) should researchers adjust for a variable indicating if a patient had a filling in a molar in the previous 18 months? Why or why not?

g.If the controls were patients who also had a molar filling is the OR a good estimate of the RR? Why or why not?

h.Discuss both 1 strength and 1 weakness of this study design (assume they used anyone with a root canal in this practice the last 18 month as cases and any patient from this practice who did not as controls and controls are the same ages as cases)

EXTRA CREDITName one thing you would do to improve the study (as described in h. above) and explain how it would improve the study.

exposure Cases Controls OR Have gum disease 15 10 Chew sugarless gum 6 20 Floss regularly 10 65 Taken antibiotics in 5 36 previous 6 months Overweight/obese 20 38 Recent viral infection 17 51